1. Field of the Invention
The present invention relates to a contour compensation. More specifically, the present invention relates to a method, a program, and a circuit for performing a contour compensation of an object in an image. Additionally, the present invention relates to an image signal display device.
2. Description of Relevant Art
Conventionally, a contour compensation circuit, which strengthen a contour of an object (a contour strengthen object) in an image, as shown in FIG. 10, has a contour compensation signal generator, a retarder, and an accumulator.
The contour compensation signal generator consisting of high-pass filter generates a contour compensation signal from an input signal (an input image signal), which is obtained from an image pickup of an object, and outputs the contour compensation signal to the accumulator. The input signal entered to the retarder is delayed for arbitrary seconds, and then entered to the accumulator.
The accumulator generates a contour-compensated signal by adding the contour compensation signal to the input signal entered from the retarder.
When the input signal is entered to the contour compensation circuit, the input signal is branched, and then entered to each of the contour compensation signal generator and the retarder.
The contour compensation circuit, finally, generates the contour-compensated signal after the processing of the input signal in the contour compensation signal generator, the retarder, and the accumulator. Thus, the image, in which the contour of the object is emphasized, is displayed on an image signal display device (hereinafter indicated as display device) based on the contour-compensated signal.
Here, the relation between the brightness level (signal level) at the time of contour compensation and the position in the display device is shown in FIG. 11.
FIG. 11A indicates the change of the brightness level of the contour region on the display device without the contour compensation.
FIG. 11B indicates the change of the brightness level of the contour-emphasized region on the display device after performing the contour compensation.
In other words, FIG. 11A shows the change of the brightness level of the contour region, which will be emphasized by the contour compensation, on the display device, before adding the contour compensation signal to the input signal (image signal) FIG. 11B shows the change of the brightness level of the contour-emphasized region on the display device after adding the contour compensation signal to the input signal (image signal)
In this FIG. 11A and FIG. 11B, the maximum level (Lmax) is a maximum brightness value (upper limit) that can be displayed (indicated) on the display device. The minimum level (Lmin) is a minimum brightness value (lower limit) that can be displayed (indicated) on the display device.
Additionally, the signal shown in the circle indicated with a dot-dash line corresponds to the contour compensation signal at about a time (n+m). Xn+m is a signal level of the display device driven by the input signal at the time (n+m). h(xn+m) is a signal level of the display device driven by the contour-compensated signal, which is generated at the time (n+m).
Here, these signals are generated by utilizing an out-of-green method. In this out-of-green method, G (Green) signal is obtained from the input signal (input image signal) by utilizing a high-pass filter, which allows to pass the high-region of the G (green) of RGB that is the three primary colors of the color. Then, the correction of R (Red) signal and B (blue) signal, which are contained in the input signal, is performed by utilizing the obtained G (Green) signal as standard. Hereinafter, this G (Green) channel is indicated as standard channel.
This out-of-green method is widely used when the display of the image on the display device is performed by utilizing three-sensor pickup method(three image device system). That is, this out-of-green method is used when the image is displayed on the display device by utilizing 3 pixels, R signal (R pixels) G signal (G pixels), and B signal (B pixels), of three image device system.
In this out-of-green method, since the color of G (green) gives strong influences on the enhancement of the outline of the object in the image, the color of G (green) is used as standard.
In other words, in the contour compensation utilizing the difference of a luminosity level, since the enhancement of the outline of the object is affected by the brightness of the color of G (Green), the color of G (Green) is used as the standard.
In the conventional contour compensation circuit, as shown in FIG. 11B, if the image display is performed based on the contour-compensated signal, the required brightness level of the display device may exceed the maximum level (shown by dot-dash line). Here, as shown in FIG. 11B, since the region exceeding limit level cannot be displayed at the projected brightness, the region exceeding limit level (maximum level) is commonly referred to as “clip (white clip)”. When this clip arises, the region near the boundary of the object in the image seems to have colored. This phenomenon as a result of the clip is referred to as “false coloring phenomenon”.
Generally, the wave profile of the contour compensation signal changes by turns from plus to minus or from misus to pluse. Thus, the sum total of the contour compensation signal is zero.
If one side of the contour compensation signal exceeds the limit of the display device and other side of the contour compensation signal does not exceeds the limit of the display device, the sum total of the contour compensation signal is not equal to zero.
In this case, the signal level of the region near the boundary of the object in the image may be changed and the region near the boundary seems to have colored.
Moreover, when the image pickup of the object is performed using the four pixel offset method utilizing the out-of-green method, the unfavorable problems may occur. As examples of this unfavorable problems, the long processing time for the processing of the image signal, and the requirement of the large hardware size of the circuit, are cited.
Here, in the four pixel offset method, the image pickup and display is performed using the device, which handles the image by utilizing input signal composed of R (Red) channel, G1 (Green 1) channel, B (Blue) channel, and G2 (Green 2) channel.
In this device, the pixels of G1 (Green 1) and the pixels of G2 (Green 2) are arrayed so that the position of each pixel of G1 (Green 1) is displaced in the horizontal and the vertical direction with respect to each pixel of G2 (Green 2). Here, the amount of the displacement is ½ of a pixel pitch.
Thereby, the display device adopting this arrangement has an improved resolution.
As reasons described above, a method and program for performing the contour compensation, a circuit for processing an image signal in order to perform the contour compensation, and an image signal display device adopting the contour compensation circuit have been required.